Power supply system for a camera

ABSTRACT

A power supply system for a camera supplies electrical power to a light measuring circuit, a display circuit and others. During a hold state before the camera turns into a standby state, the power supply system supplies a boosted electrical power intermittently to the light measuring circuit, the display circuit and others, so that photographic information such as shutter speed and aperture value based on the measurement of the light measuring circuit are displayed on a display and power consumption in the hold state can be made small.

This application is a divisional of application Ser. No. 07/352,290,filed May 15, 1989.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a power supply system for a camerawhich supplies electrical power to a light measuring circuit, a displaycircuit and others in a hold state which is held during a predeterminedperiod of time before the camera turns into a standby state, and acamera system to control the operation of the light measuring circuitand the display circuit in the hold state.

2. Description of the Prior Art

Conventional cameras, having a display panel for displaying photographicinformation such as aperture value and shutter speed, turns into astandby state through a hold state held during a predetermined period oftime. In the hold state of the conventional cameras a light measuringcircuit, a display circuit and their control circuits are operating asusual. The purpose of the hold state is to facilitate a settingoperation of the photographic information or confirmation of it after ashutter is released.

FIG. 2 shows an example of a power supply system for a camera of aconventional type. In FIG. 2, B is a battery as a power supply source; 1is a power supply circuit; 2 is a booster circuit comprising a DC/DCconverter etc. in the circuit 1; 3 is a control circuit comprising amicrocomputer including a RAM which controls camera operation and alsomemorizes data such as photographing conditions (shutter speed, aperturevalue, etc.) in the RAM; 4 is a display circuit using a liquid crystaldevice; 5 is a motor driving circuit; 6 is a motor for driving a lensetc.; 7 is a switch to start the control operation of the microcomputerin the circuit 3.

An input terminal Vin of power supply circuit 1 is connected to apositive electrode of the battery B; an output terminal Vout in thepower supply circuit 1 is connected to power supply input terminals Vcc1and Vcc2 of the control circuit 3 and the display circuit 4respectively, and also connected to an anode of a voltage regulatingdiode D4 through a resistor R2; the anode of the diode D4 is connectedto a reference voltage terminal Vr of the display circuit 4 and thecathode is grounded; a power supply control terminal PWC of the controlcircuit 3 is connected to a control terminal Vc of the power supplycircuit 1.

The positive electrode of the battery B is connected to a power supplyinput terminal Vcc3 of the motor driving circuit 5 and to an anode of alight emitting diode (LED) D3; a cathode of the diode D3 is connected tothe display circuit 4 through a resistor R1; the motor driving circuit 5is a load circuit which necessitates comparatively large current andtherefore electrical power is directly supplied from the battery B.

The power supply circuit 1 is explained in the following: an inputterminal IN of the booster circuit 2 is connected to the input terminalVin of the power supply circuit 1, and an output terminal OUT of thebooster circuit 2 is connected to the output terminal Vout of powersupply circuit 1 through the diode D2; a control terminal C of thebooster circuit 2 is connected to a control terminal Vc of the powersupply circuit 1; the input terminal Vin of the power supply circuit 1is connected to the anode of the diode D1, and the cathode of the diodeD1 is connected to the output terminal Vout of the power supply circuit1.

An OR circuit relating to the booster circuit 2 and the battery B isconstituted by the diode D1 and the diode D2, and the circuit is soconstituted that the output voltage of either of the two, the boostercircuit 2 or the battery B, which has a higher voltage is output fromthe output terminal Vout.

The operation of the power supply circuit 1 is explained in thefollowing: when the switch 7 is OFF and the control circuit 3 is notstarted, a control signal "HIGH" is output from the power supply controlterminal PWC of the control circuit 3 to the power supply circuit 1, andthe booster circuit 2 in the power supply circuit 1 is not in operatingstate; at this time, the voltage of the battery B is output to theoutput terminal Vout of the power supply circuit 1 through the diode D1and it is supplied to the power input terminals Vcc1 and Vcc2 of thecontrol circuit 3 and the display circuit 4, and the memory contents ofthe RAM in the control circuit 3 are held by the battery power; thevoltage of the battery B is applied to the anode of the voltageregulating diode D4 and a reference voltage for driving the liquidcrystal device is generated by the diode D4 and it is input to thereference voltage input terminal Vr of the display circuit 4; if thevoltage of the battery B is lowered, it may cause the hold of the memorycontents in the RAM impossible or the lowering the reference voltage,which degrades the contrast of display on the liquid crystal device.

The power for the motor driving circuit 5 and the light emitting diodeD3 are supplied from the battery B independent of ON or OFF of theswitch 7.

When the switch 7 is turned ON, a signal "LOW" is output from the powersupply control terminal PWC and supplied to the control terminal Vc ofthe power supply circuit 1 to start the booster circuit 2 in the powersupply circuit 1. At this time, the output voltage of the boostercircuit 2, in which the battery voltage is boosted, is output to theoutput terminal Vout of the power supply circuit 1 through the diode D2and is supplied to the respective power supply terminals Vcc1 and Vcc2of the control circuit 3 and display circuit 4 and the microcomputer inthe control circuit 3 starts the control operation. The output voltageof the booster circuit 2 is also applied to the anode of the voltageregulating diode D4 through the resistor R2 and the reference voltagefor driving the liquid crystal device is generated by the diode D4.

When the sequence of the control operation of the microcomputer isadvanced to the step in which the motor 6 for driving the lens etc. isdriven, a large current flows in the motor driving circuit 5 and thevoltage of the battery B is lowered; it causes to lower the appliedvoltage to the light emitting diode D3 and the brightness of the diodeD3 is lowered. After that, when the control operation of themicrocomputer is finished, the control signal "HIGH" is output from thepower supply control terminal PWC of the control circuit 3 and suppliedto the booster circuit 2 and then the operation of the circuit 2 isstopped, and the voltage of the battery is supplied to the controlcircuit 3, display circuit 4 and the voltage regulating diode D4 throughthe diode D1 in the power supply circuit 1.

Furthermore, since the control circuit 3, the display circuit 4 and thelight measuring circuit (not shown) are supplied the electrical power asusual during the hold state, the electricity consumption during the holdstate cannot be neglected.

As for the ways of decreasing power consumption, following examples areknown to the public: a means wherein when an automatic exposure settingis held, the power supply to a measuring circuit is stopped (for exampleJapanese Patent laid-open No. 78429/85); a means wherein when a lightmeasurement switch is kept ON for a certain time, the power supply tothe light measuring circuit is cut off and the power supply is resumedwith the ON of a shutter release switch (for example Japanese Patentlaid-open No. 78430/85 and No. 78431/85); a means wherein power issupplied periodically in a fixed period during a light measuring switchis kept ON (Japanese Patent laid-open No. 140326/85).

In these known power supply system, matters after a light measurementswitch is turned OFF are not taken into consideration. Therefore, therestill remained a problem to be solved on the cut down of the powerconsumption to lengthen the time of the hold state.

SUMMARY OF THE INVENTION

A main object of the present invention is to provide an improved powersupply system which can reduce power consumption in the hold time, andlengthen the hold time.

Another object of the present invention is to provide an improved powersupply system which can supply stable electric power to the lightmeasuring circuit and the display circuit.

A further object of the present invention is to provide an improvedcamera system which can control the operation of the light measuringcircuit and display circuit with low power consumption in the holdstate.

These and other objects will become apparent from the following detaileddescription taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a power supply system for a camera in an embodiment of thepresent invention.

FIG. 2 shows a power supply system for a camera of a conventional type.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention is explained referring to FIG. 1in the following. In FIG. 1, similar symbols are used for similarmembers to those in FIG. 2 in which a prior art is explained.

An input terminal Vin of a power supply circuit 11 is connected to apositive electrode of a battery B; an output terminal Vout1 of the powersupply circuit 11 is connected to respective power supply inputterminals Vcc1 and Vcc2 of a control circuit 3 and a display circuit 4;an output terminal Vout2 of the power supply circuit 11 is connected toan anode of a light emitting diode D3, and also connected to a voltageregulating diode D4 through a resistor R2; the anode of the diode D4 isconnected to a reference voltage terminal Vr of the display circuit 4and its cathode is grounded. All load circuits connected to the outputterminal Vout2 require a stabilized voltage.

A constitution in which the battery B, a motor driving circuit 5 whichconsumes a large power, the control circuit 3 and the display circuit 4are connected to each other is the same as that shown in FIG. 2.

In the power supply circuit 11, an input terminal IN1 of a boostercircuit 2 comprising a voltage regulator and an input terminal IN2 of avoltage stabilizing circuit 12 comprising a DC/DC converter etc. areconnected to the input terminal Vin; an output terminal OUT2 of thevoltage stabilizing circuit 12 is connected to the output terminal Vout2of the power supply circuit 11 through a diode D1; a control terminal Cof the booster circuit 2 is connected to a control terminal Vc of thepower supply circuit 11; an output terminal OUT1 of the booster circuit2 is connected to an anode of a diode D2 and to an anode of a diode D5;the cathodes of the diode D2 and the diode D5 are respectively connectedto the output terminals Vout1 and Vout2 of the power supply circuit 11;the cathode of diode D1 is connected to an anode of a diode D6; acathode of the diode D6 is connected to the cathode of the diode D2.

In other words, an OR circuit relating to the output voltages of thebooster circuit 2 and the voltage stabilizing circuit 12 is constitutedwith the diode D1 and the diode D5 and another OR circuit relating tothe output voltages of the booster circuit 2 and the voltage stabilizingcircuit 12 is constituted with the diode D2 and the diode D6. Therefore,one of either of the two, the output voltage of the booster circuit 2through the diode D2 or that of the voltage stabilizing circuit 12through the diode D6, which has a higher voltage is output from theoutput terminal Vout 1. On the other hand, from the output terminal Vout2, one of either of the two, the output voltage of the booster circuit 2through the diode D5 or that of the voltage stabilizing circuit 12through the diode D1, which has a higher voltage.

A light measuring circuit 8 is provided in this embodiment, whichreceives the output of a light receiving element PC and is controlled bythe control circuit 3; electrical power necessary for the lightmeasuring circuit 8 is supplied to its input terminal Vcc3 from theoutput terminal Vout3 of the power supply circuit 11; the outputterminal OUT3 of the booster circuit 2 is also connected to the outputterminal Vout3. When a switch 7, which is used for starting lightmeasuring operation etc., is turned ON, the control circuit 3 controls acontrol signal output from a power supply control terminal PWC to be"LOW", and when the switch 7 is turned OFF or a control operation of thecontrol circuit 3 is finished, the control circuit 3 controls the camerato be in a hold state. Under this state, the control signal output fromthe power supply control terminal PWC changes over to "LOW"intermittently from "HIGH" during a fixed time determined by a timerbuilt-in or attached outside in the control circuit 3.

The operation of the power supply system is explained. When the switch7, which is used for starting of light measuring operation etc., is in aOFF state and the control circuit 3 is not started yet, the controlsignal "HIGH" is output from the power supply control terminal PWC ofthe control circuit 3 to the power supply circuit 11, and in that statethe booster circuit 2 in the power supply circuit 11 is not in operatingstate; at this time the voltage stabilizing circuit 12 is operating tostabilize the voltage of the battery B and its output voltage is outputto the output terminal Vout2 through diode D1; the output voltage outputto the Vout2 is also output to Vout1 through diode D6; from these outputterminals Vout1 and Vout2 the output voltage of the voltage regulatingcircuit 12 is supplied to the anode of the light emitting diode D3 andto the anode of the voltage regulating diode D4 through the resistor R2,and is also supplied to the power supply input terminals Vcc1 and Vcc2of the control circuit 3 and the display circuit 4. By the outputvoltage of the voltage stabilizing circuit 12, the memory contents in aRAM in the control circuit 3 is held and the liquid crystal referencevoltage for driving a liquid crystal device in the display circuit 4 isgenerated in the voltage stabilizing diode D4 to be supplied to thereference voltage input terminal Vr.

When the switch 7 is turned ON, the control signal "LOW" is output fromthe power supply control terminal PWC of the control circuit 3 and it issupplied to the control terminal Vc of the power supply circuit 11 andthen the booster circuit 2 in the power supply circuit 11 starts itsoperation; at this time an output voltage of the booster circuit 2, aboosted voltage of the battery voltage, is output to the output terminalVout1 of the power supply circuit 11 through the diode D2 and applied topower supply input terminals Vcc1 and Vcc2 of the control circuit 3 anddisplay circuit 4; then the microcomputer which constitute the controlcircuit 3 starts the control operation; the output voltage of thevoltage stabilizing circuit 12 is output from the output terminal Vout2of the power supply circuit 11 through the diode D1 and supplied to thelight emitting diode D3 and to the voltage regulating diode D4.

While the light measuring circuit 8 is held in its operating state bythe control operation of the microcomputer, and a measuring data is readperiodically at a predetermined frequency from the light measuringcircuit 8 by the microcomputer. The microcomputer calculates theexposure data such as aperture value and shutter speed based on thelight measuring data and outputs the calculated exposure data to thedisplay circuit in the same frequency as the frequency of reading thelight measuring data.

The frequency of reading the light measuring data is shorter than thefrequency that the control signal output from the power supply controlterminal PWC changes over to "LOW" intermittently from "HIGH" in thehold state.

In the next step, when the control operation by the microcomputer isadvanced and the motor 6 is driven to drive a lens etc., a large currentflows in the motor driving circuit 5 and the voltage of the battery B islowered for a time, so that the input voltage of the voltage stabilizingcircuit 12 is lowered and stops its stabilizing operation, at this timethe output voltage of the booster circuit 2 is output to the outputterminal Vout2 through diode D5 and it is supplied to the light emittingdiode D3 and the voltage regulating diode D4. By this arrangement, eventhough the voltage of the battery B is lowered, the brightness of thelight emitting diode D3 is not lowered and also the reference voltagefor driving the liquid crystal device generated by the voltageregulating diode D4 is not lowered; the contrast of display on theliquid crystal device is therefore not degraded.

After that the switch 7 is turned OFF or the control operation of themicrocomputer is finished, the camera is turned into the hold state.

According to the present invention, electric power is intermittentlysupplied in the hold state. That is, the control circuit 3 operates tooutput the control signals "LOW" intermitently in a predetermined periodof time. Interlocking with the signal "LOW", the electric power issupplied to the light measuring circuit 8 and the display circuit 4 tobe started their operation and interlocking with the signal "HIGH" aboveoperation is stopped, so that the camera repeats start and stand-by inthe hold state. The exposure data such as shutter speed and aperturevalue data in the hold state is renewed at each start.

In this embodiment, even when the control signal "HIGH" is output fromthe power supply control terminal PWC and the operation of the boostercircuit is stopped, the output voltage Vout2 of the voltage stabilizingcircuit 12 of the power supply circuit 11 is supplied to the controlcircuit 3, the display circuit 4, the light emitting diode D3 and thevoltage regulating diode D4. It is therefore possible to supply a stableconstant voltage to the display circuit 4 and the light emitting diodeD3 in spite of repeated start and stop of the camera.

As described in the above according to the present invention, in thehold state of the camera, the electric power is supplied to the lightmeasurement circuit and the display circuit intermittently in a fixedperiod, so that power consumption in a hold state can be decreased andit is thereby made possible to lengthen the hold time to helpphotographers confirm the photographing information.

What is claimed is:
 1. An electrical power supply system in a camera,comprising:(a) a power source; (b) a DC/DC converter, connected to saidpower source, for converting a voltage of said power source into apredetermined voltage and supplying the predetermined voltage; (c) avoltage regulator, connected to said power source in parallel with saidDC/DC converter, for supplying a regulating voltage; and (d) a controlcircuit connected to said DC/DC converter and said voltage regulator,said control circuit being supplied the predetermined voltage from saidDC/DC converter or the regulating voltage from said voltage regulator.2. An electrical power supply system as claimed in claim 1, furthercomprising:(e) selecting means connected to said DC/DC converter andsaid voltage regulator for supplying alternatively the predeterminedvoltage or the regulating voltage to said control circuit.
 3. Anelectrical power supply system as claimed in claim 2, wherein saidcontrol circuit is a microcomputer.
 4. An electrical power supply systemas claimed in claim 3, wherein said microcomputer has a volatile memorymemorizing photographic information.
 5. An electrical power supplysystem as claimed in claim 2, wherein said selecting means consists of aplurality of diodes.
 6. An electrical power supply system as claimed inclaim 3, further comprising:(f) switching means having a first state anda second state and arranged to be operable manually; wherein saidselecting means outputs the predetermined voltage when said switchingmeans is in the first state and supplies the regulating voltage whensaid switching means is in the second state.
 7. An electrical powersupply system as claimed in claim 6, wherein said microcomputer starts aprogrammed sequence in response to fact that said switching meanschanges into the first state from the second state.
 8. An electricalpower supply system as claimed in claim 6, wherein said microcomputerstarts a programmed sequence intermittently during a lapse of thepredetermined time after said switching means is in the second state. 9.An electrical power supply system as claimed in claim 1, furthercomprising:(g) a load circuit connected to said DC/DC converter and saidvoltage regulator, said load circuit being supplied the predeterminedvoltage from said DC/DC converter or the regulating voltage from saidvoltage regulator.
 10. An electrical power supply system as claimed inclaim 9, further comprising:(h) second selecting means connected to saidDC/DC converter and said voltage regulator for supplying alternativelythe predetermined voltage or the regulating voltage to said loadcircuit.
 11. An electrical power supply system as claimed in claim 10,wherein said second selecting means outputs the regulating voltage ingeneral but supplies the predetermined voltage when the regulatingvoltage lowers.